To prevent leakage of body exudates from absorbent articles such as feminine care pads or napkins and disposable diapers, it is desirable that the exudates not reach the edges of the absorbent material in the article. A xe2x80x9ccenter fillxe2x80x9d strategy is desirable for leakage control, wherein fluids are preferentially held in a central region of the article. Unfortunately, in traditional absorbent articles, there is generally no means to maintain good fit of the article against the body of the wearer in use, especially once the article is wet. Though simple articles with deflection elements have been proposed, improved deflection means in cooperative relationship with multiple discrete elements of an absorbent core do not appear to be known. What is needed is an article with good center fill performance that can maintain good body fit even when the article is wet. Further, what is needed is an article with multiple absorbent elements offering excellent body fit through a three-dimensional topography that becomes more pronouncedly three-dimensional when the article is worn and compressed between the legs of the wearer while still maintaining comfort.
It has been discovered that improved body fit and leakage control can be obtained in absorbent articles by providing an absorbent core comprising two discrete absorbent members operatively associated with a central rising member. The central rising member, described more fully hereafter, is an element which deflects upwards when laterally compressed from the side. The two discrete members of the absorbent core are the central absorbent member, which serves as the primary intake member and body-contacting element, and the outer absorbent member which surrounds the central absorbent member at least along the longitudinal sides thereof. The outer absorbent member can be both wider and longer than the central absorbent member, and has a central void therein for receiving at least a portion of the central absorbent member and optionally for receiving the central rising member. The absorbent members of the absorbent core can be formed from any known absorbent material such as cellulosic fibrous webs and the like.
In the target zone of the article where fluid intake occurs, a break exists between the central absorbent member and the outer absorbent member which assists in governing effective deformation of the article when the article is compressed laterally and when the central rising member deflects upwardly. Upward deflection of the central rising member is sufficient to deflect the central absorbent member toward the body, desirably without substantially deflecting the outer absorbent member. Lateral compression of the article by the body of the user thus establishes a W-shaped cross-section of the article in the target zone as the outer sides of the outer absorbent member deflect like the outer legs of a xe2x80x9cWxe2x80x9d and the central absorbent member is deflected in the shape of an inverted xe2x80x9cVxe2x80x9d or inverted xe2x80x9cUxe2x80x9d to generally give an overall xe2x80x9cWxe2x80x9d-shape characteristic to the article, which is particularly valuable for good conformance to female anatomy. Thus, the interaction between the discrete members of the absorbent core and the central rising member during conditions of use result in an article with excellent body fit characteristics during use.
The absorbent article further comprises a topsheet and a backsheet connected to the topsheet, with the absorbent core and central rising member disposed therebetween.
The outer absorbent member typically serves as a frame or shaping element for the absorbent article and serves as a backup absorbent reservoir to receive fluid from the central absorbent member. Desirably, the outer absorbent member has a pore size greater than the pore size of the central absorbent member in the regions where the two members are likely to contact to encourage fluid to remain in the central absorbent member. Alternatively, the contact region between the two members may be treated with hydrophobic matter such as a silicone spray, impregnated wax, nonwetting fibers, or other means to reduce wicking between the two members, thus forming a wicking impediment.
The central rising member is disposed below the central absorbent member or can form part of the central absorbent member itself, being disposed therein. In use, the central rising member is capable of upwardly deflecting the absorbent material in the central absorbent member that lies above the central rising member.
Further improvements in body fit and deformation of the article in use can be achieved by adding additional features to the articles of the present invention. For example, improved deformation can also be promoted or assisted by one or more shaping lines and/or one or more crease lines in the absorbent core. A crease line lies away from the longitudinal centerline and promotes downward folding or bending of the article along the crease line (e.g., a valley fold) during lateral compression from the longitudinal sides of the article. A shaping line resides in the central absorbent member and promotes upward folding or bending (e.g., a mountain fold) during lateral compression from the longitudinal sides of the article. A shaping line coupled with at least two crease lines works to establish a W-fold geometry in the article when laterally compressed, offering good control over the upward deflection of a central absorbent member in the absorbent core. Crease lines and shaping lines, as defined therein, will be generally referred to hereafter as xe2x80x9cbending lines.xe2x80x9d
Hence, in one aspect, the invention resides in an absorbent article having two longitudinal sides and a target zone, comprising:
a) a liquid impervious backsheet;
b) a liquid pervious topsheet attached to the backsheet;
c) an absorbent core positioned between the topsheet and the backsheet, the absorbent core comprising an outer absorbent member and a central absorbent member, the outer absorbent member having a width in the target zone greater than the width of the central absorbent member in the target zone and having a central void for receiving at least a portion of the central absorbent member, the absorbent core further comprising a central rising member disposed beneath the central absorbent member, whereby lateral compression of the absorbent core from the longitudinal sides causes the central rising member to deflect the central absorbent member away from the backsheet.
In another aspect, the invention resides in an absorbent article for use on the body of a wearer, the article having two longitudinal sides and a target zone, comprising:
a) a liquid impervious backsheet;
b) a liquid pervious topsheet attached to the backsheet;
c) an absorbent core positioned between the topsheet and the backsheet, the absorbent core comprising an outer absorbent member and a central absorbent member, the outer absorbent member having a width in the target zone greater than the width of the central absorbent member in the target zone and having a central void for receiving at least a portion of the central absorbent member, the absorbent core further comprising a central inflatable member disposed within the absorbent core adapted to deflect the central absorbent member away from the backsheet when activated by the wearer.
In another aspect, the invention resides in an absorbent article comprising a topsheet, a backsheet joined to the topsheet, an absorbent core disposed between the backsheet and the topsheet, the absorbent core comprising an outer absorbent member and a central absorbent member operatively associated with a central rising member, the central rising member having longitudinal sides and a longitudinally central hinge dividing the central rising member into a first portion and second portion, the article further comprising attachment means in cooperative relationship with the central rising member, wherein application of inwardly lateral compressive force to the longitudinal sides of the central rising member causes the central rising member to deflect upward along the longitudinally central hinge, and wherein the attachment means holds the central rising member in an upwardly deflected state when the inwardly lateral compressive force is relaxed.
In yet another aspect, the invention resides in a method for producing an absorbent article having a central absorbent member, the method comprising:
a) preparing an outer absorbent member, wherein the outer absorbent member has a central void;
b) disposing a central absorbent member in the central void;
c) disposing a central rising member beneath the central absorbent member;
d) disposing a backsheet beneath the central rising member and beneath the outer absorbent member;
e) disposing a topsheet above the central absorbent member and the outer absorbent member; and
f) attaching the topsheet to the backsheet.
In another aspect, the invention resides in a method for producing an absorbent article comprising:
a) preparing an outer absorbent member, wherein the outer absorbent member has a central void;
b) disposing a central rising member in the central void;
c) inserting an absorbent material into the central void to form a central absorbent member.
The above method can further comprise disposing a backsheet beneath the absorbent core; disposing a topsheet above the absorbent core; and attaching a portion of the topsheet to a portion of the backsheet.
Possible uses of the present invention include absorbent articles for intake, distribution, and retention of human body fluids. Examples include feminine care pads and related catamenial devices or sanitary napkins, including xe2x80x9cultra-thinxe2x80x9d pads and pantiliners and maxipads. Likewise, the present invention can be applied to diapers, disposable training pants, other disposable garments such as swimming garments, incontinence articles, bed pads, medical absorbents, wound dressings or other absorbent articles. The articles of the present invention provide significant leakage protection, fluid center-fill absorptive performance, and other desirable attributes for absorbent articles.
xe2x80x9cAbsorbency Under Loadxe2x80x9d (AUL) is a measure of the liquid retention capacity of a material under a mechanical load. It is determined by a test which measures the amount in grams of an aqueous solution, containing 0.9 weight percent sodium chloride, a gram of a material can absorb in 1 hour under an applied load or restraining force of about 2 kPa (0.3 pound per square inch).
The AUL apparatus comprises a Demand Absorbency Tester (DAT) as described in U.S. Pat. No. 5,147,343, issued Sep. 15, 1992 to Kellenberger, herein incorporated by reference, which is similar to a GATS (Gravimetric Absorbency Test System), available from M/K Systems, Danners, Mass.
As used herein, a material is said to be xe2x80x9cabsorbentxe2x80x9d if it can retain an amount of water equal to at least 100% of its dry weight as measured by the test for Intrinsic Absorbent Capacity given below (i.e., the material has an Intrinsic Absorbent Capacity of at about 1 or greater). Desirably, the absorbent materials used in the absorbent members of the present invention have an Intrinsic Absorbent Capacity of about 2 or greater, more specifically about 4 or greater, more specifically still about 7 or greater, and more specifically still about 10 or greater, with exemplary ranges of from about 3 to about 30 or from about 4 to about 25 or from about 12 to about 40.
As used herein, xe2x80x9cabsorbent capacityxe2x80x9d refers to the total mass of water that a specified quantity of absorbent material can hold, and is simply the Intrinsic Absorbent Capacity multiplied by the dry mass of the absorbent material. Thus 10 g of material having an Intrinsic Absorbent Capacity of 5 has an absorbent capacity of 50 g (or about 50 ml of fluid).
As used herein, xe2x80x9cbulkxe2x80x9d and xe2x80x9cdensity,xe2x80x9d unless otherwise specified, are based on an oven-dry mass of a sample and a thickness measurement made at a load of 0.34 kPa (0.05 psi) with a 7.62-cm (three-inch) diameter circular platen. Thickness measurements of samples are made in a TAPPI-conditioned room (50% relative humidity and 23xc2x0 C.) after conditioning for at least four hours. Samples should be essentially flat and uniform under the area of the contacting platen. Bulk is expressed as volume per mass of fiber in cc/g and density is the inverse, g/cc.
As used herein, the term xe2x80x9ccellulosicxe2x80x9d is meant to include any material having cellulose as a major constituent, and specifically comprising at least 50 percent by weight cellulose or a cellulose derivative. Thus, the term includes cotton, typical wood pulps, nonwoody cellulosic fibers, cellulose acetate, cellulose triacetate, rayon, thermomechanical wood pulp, chemical wood pulp, debonded chemical wood pulp, milkweed, or bacterial cellulose.
As used herein, xe2x80x9cCentral Elevationxe2x80x9d is defined as the height difference between the center of the central absorbent member along the transverse centerline of the article and the average height of the longitudinal sides of the central absorbent member along the transverse centerline of the article at the end of the Vertical Deformation Test hereinafter described. The Central Elevation for absorbent articles of the present invention can be at least about 0.5 cm, specifically at least about 1 cm, and more specifically at least about 1.2 cm and up to about 10 cm. Desirably, an absorbent article of the present invention exhibits an increase in Central Elevation in the crotch region of at least about 20%, and more specifically at least about 50%, relative to the Central Elevation in the crotch region exhibited by an essentially identical absorbent article without a shaping line.
As used herein, the xe2x80x9ccrotch regionxe2x80x9d of an absorbent article refers to the generally central region that will be in contact with the crotch of the user, near the lowermost part of the torso, and resides between the front and rear portions of the article. Typically the crotch region contains the transverse centerline of the article and generally spans approximately 7 to 10 cm in the longitudinal direction.
Many articles of the present invention are intended to be worn in the crotch of a wearer, and thus have crotch regions. However, the present invention can also be applied to other articles such as underarm pads or wound dressings where a crotch region may not exist. In such cases, the article will have a region where fluid intake is intended to occur, termed the xe2x80x9ctarget region.xe2x80x9d The portion of the article including the longitudinal length of the target region and the full transverse width of the article normal to length of the target region is defined herein as the xe2x80x9ctarget zone.xe2x80x9d For articles intended to be worn in the crotch, the terms xe2x80x9ctarget zonexe2x80x9d and xe2x80x9ccrotch regionxe2x80x9d are generally synonymous, whereas xe2x80x9ctarget regionxe2x80x9d generally excludes the portions of the absorbent core near the longitudinal sides since the intended area for fluid intake is generally substantially central in the absorbent article.
As used herein, the term xe2x80x9cextensiblexe2x80x9d refers to articles that can increase in at least one of their dimensions in the x-y plane by at least 10% and desirably at least 20%. The x-y plane is a plane generally parallel to the faces of the article. The term extensible includes articles that are stretchable and elastically stretchable (defined below). In the case of a sanitary napkin comprising an absorbent core, for example, the article and the absorbent core are desirably extensible both in length and width. The absorbent article, however, may only be extensible in one of these directions. Preferably, the article is extensible at least in the longitudinal direction. Examples of extensible materials and articles, and their methods of preparation, are disclosed in U.S. Pat. No. 5,611,790, issued Mar. 18, 1997 to Osborn.
As used herein, a bulk material (e.g., the absorbent components of the article or the material providing shape in the outer shaping member) is considered xe2x80x9cflexiblexe2x80x9d if a straight, TAPPI-conditioned (50 percent relative humidity at 23xc2x0 C.) strip of the material 25 cm long with a cross-section of 1 cmxc3x971 cm can be bent 1800 around a 5-cm diameter rod without breaking and without requiring application of more than 6 Newtons of force to the ends of the strip to cause the bending over a 3-second span of time.
As used herein, the term xe2x80x9cflexure-resistantxe2x80x9d refers to an element which will support a bending moment, in contrast to an element which will support only axial forces. Likewise, as used herein, xe2x80x9cflexure resistancexe2x80x9d is a means of expressing the flexibility of a material or article and is measured according to the Circular Bend Procedure described in detail in U.S. Pat. No. 5,624,423, issued Apr. 29, 1997 to Anjur et al., herein incorporated by reference in its entirety. Flexure resistance is actually a measurement of peak bending stiffness modeled after the ASTM D4032-82 Circular Bend Procedure. The Circular Bend Procedure of Anjur et al. is a simultaneous multidirectional deformation of a material in which one face of a specimen becomes concave and the other face becomes convex. The Circular Bend Procedure gives a force value related to flexure-resistance, simultaneously averaging stiffness in all directions. For comfort, the absorbent article desirably has a flexure-resistance of less than or equal to about 1,500 grams, more specifically about 1000 grams or less, more specifically still about 700 grams or less and most specifically about 600 grams or less. For shaping performance, the central absorbent member as well as the outer absorbent member can have a flexure resistance of at least about 30 grams, more specifically at least about 50 grams, and most specifically at least about 150 grams.
As used herein, xe2x80x9cFree Swell Capacityxe2x80x9d (FS) is the result of a test which measures the amount in grams of an aqueous solution, containing 0.9 weight percent sodium chloride, that a gram of a material can absorb in 1 hour under negligible applied load. The test is done as described above for the AUL test, except that the 100 gm weight used in the AUL test is not placed on the sample.
The Free Swell Capacity of the materials of the present invention can be above 8, more specifically above 10, more specifically above 20, and most specifically above 30 grams/gram.
As used herein, xe2x80x9cFree Swell:AUL Ratioxe2x80x9d is the ratio of Free Swell Capacity to AUL. It will generally be greater than one. The higher the value, the more sensitive the material is to compressive load, meaning that the sample is less able to maintain its potential pore volume and capillary suction potential under load. Desirably, the materials of the present invention have xe2x80x9cFree Swell:AUL Ratioxe2x80x9d of about 4 or less, more specifically about 2 or less, more specifically still about 1.5 or less, and more specifically about 1.3 or less, with an exemplary range of from about 1.2 to about 2.5.
As used herein, xe2x80x9chigh yield pulp fibersxe2x80x9d are those papermaking fibers of pulps produced by pulping processes providing a yield of about 65 percent or greater, more specifically about 75 percent or greater, and still more specifically from about 75 to about 95 percent. Yield is the resulting amount of processed fiber expressed as a percentage of the initial wood mass. High yield pulps include bleached chemithermomechanical pulp (BCTMP), chemithermomechanical pulp (CTMP), pressure/pressure thermomechanical pulp (PTMP), thermomechanical pulp (TMP), thermomechanical chemical pulp (TMCP), high yield sulfite pulps, and high yield Kraft pulps, all of which contain fibers having high levels of lignin.
As used herein, the term xe2x80x9chorizontal,xe2x80x9d refers to directions in the plane of the article that are substantially parallel to the body-side surface of the article, or, equivalently, substantially normal to the vertical direction of the article, and comprises the transverse direction and the longitudinal direction of the article, as well as intermediate directions. The orientation of components in an article, unless otherwise specified, is determined as the article lies substantially flat on a horizontal surface.
As used herein, the term xe2x80x9chydrophobicxe2x80x9d refers to a material having a contact angle of water in air of at least 90 degrees. In contrast, as used herein, the term xe2x80x9chydrophilicxe2x80x9d refers to a material having a contact angle of water in air of less than 90 degrees.
As used herein, xe2x80x9cIntrinsic Absorbent Capacityxe2x80x9d refers to the amount of water that a saturated sample can hold relative to the dry weight of the sample and is reported as a dimensionless number (mass divided by mass). The test is performed according to Federal Government Specification UU-T-595b. It is made by cutting a 10.16 cm long by 10.16 cm wide (4 inch long by 4 inch wide) test sample, weighing it, and then saturating it with water for three minutes by soaking. The sample is then removed from the water and hung by one corner for 30 seconds to allow excess water to be drained off. The sample is then re-weighed, and the difference between the wet and dry weights is the water pickup of the sample expressed in grams per 10.16 cm long by 10.16 cm wide sample. The Intrinsic Absorbent Capacity value is obtained by dividing the total water pick-up by the dry weight of the sample. If the material lacks adequate integrity when wet to perform the test without sample disintegration, the test method may be modified to provide improved integrity to the sample without substantially modifying its absorbent properties. Specifically, the material may be reinforced with up to 6 lines of hot melt adhesive having a diameter of about 1 mm applied to the outer surface of the article to encircle the material with a water-resistant band. The hot melt should be applied to avoid penetration of the adhesive into the body of the material being tested. The corner on which the sample is hung in particular should be reinforced with external hot melt adhesive to increase integrity if the untreated sample cannot be hung for 30 seconds when wet.
xe2x80x9cPapermaking fibers,xe2x80x9d as used herein, include all known cellulosic fibers or fiber mixes comprising cellulosic fibers. Fibers suitable for making the webs of this invention comprise any natural or synthetic cellulosic fibers including, but not limited to nonwoody fibers, such as cotton, abaca, kenaf, sabai grass, flax, esparto grass, straw, jute hemp, bagasse, milkweed floss fibers, and pineapple leaf fibers; and woody fibers such as those obtained from deciduous and coniferous trees, including softwood fibers, such as northern and southern softwood kraft fibers; hardwood fibers, such as eucalyptus, maple, birch, and aspen. Woody fibers can be prepared in high-yield or low-yield forms and can be pulped in any known method, including kraft, sulfite, high-yield pulping methods, and other known pulping methods. Chemically treated natural cellulosic fibers can be used such as mercerized pulps, chemically stiffened or crosslinked fibers, or sulfonated fibers. Suitable papermaking fibers can also include recycled fibers, virgin fibers, or mixes thereof.
As used herein, a xe2x80x9cpledgetxe2x80x9d refers to an absorbent insert within an absorbent core having at least one of a width and a length smaller than the respective width and length of the absorbent core. A pledget is generally used to cause deformation or shaping of an adjoining layer of an absorbent article, and in the present invention, can be of use in shaping a pad or creating a medial hump in the pad for improved fit against the body of the wearer.
The term xe2x80x9csanitary napkinxe2x80x9d, as used herein, refers to an article which is worn by females adjacent to the pudendal region that is intended to absorb and contain the various exudates which are discharged from the body (e.g., blood, menses, and urine). While the present invention is shown and described in the form of a sanitary napkin, it should be understood that the present invention is also applicable to other feminine hygiene or catamenial pads such as panty liners, or other absorbent articles such as diapers or incontinence pads. The term xe2x80x9cfeminine care padxe2x80x9d as used herein is synonymous with sanitary napkin.
The term xe2x80x9cstretchablexe2x80x9d, as used herein, refers to articles that are extensible when stretching forces are applied to the article and offer some resistance to stretching. The terms xe2x80x9celastically stretchablexe2x80x9d or xe2x80x9celastically extensiblexe2x80x9d are intended to be synonymous. These terms, as used herein, mean that when in-plane stretching forces are removed, the article or absorbent fibrous structure will tend to return toward its unextended or unstretched dimensions (or original dimensions). It need not return all the way to its unstretched dimensions, however. It may return to relaxed dimensions between its unstretched dimensions and extended (or stretched dimensions).
As used herein, xe2x80x9cthicknessxe2x80x9d of a fluff pad or other absorbent element refers to thickness measured with a platen-based thickness gauge having a diameter of 7.62 cm at a load of about 0.05 pounds per square inch (psi) [about 35 kilograms per square meter]. The thickness of the central absorbent member or the outer absorbent member or of the absorbent article in general can be from about 2 mm to about 50 mm, more specifically from about 3 mm to about 25 mm, more specifically still from about 3 mm to about 15 mm, and most specifically from about 4 mm to about 10 mm. Ultrathin articles can have a thickness less than about 6 mm.
As used herein, the term xe2x80x9ctransversexe2x80x9d refers to a line, axis, or direction which lies within the plane of the absorbent article and is generally perpendicular to the longitudinal direction. The z-direction is generally orthogonal to both the longitudinal and transverse centerlines. The term xe2x80x9clateralxe2x80x9d refers to substantially in-plane directions having a predominately transverse component. Likewise, xe2x80x9cinwardly lateral compressionxe2x80x9d refers to compression directed from the longitudinal sides of an article toward the longitudinal centerline thereof, applied substantially in the transverse direction.
The degree of elevation of the central absorbent member can be quantified in terms of a Vertical Deformation test. As used herein, xe2x80x9cVertical Deformationxe2x80x9d refers to the height increase experienced by the body-side surface of an absorbent article when the longitudinal sides in the crotch reason are gripped and steadily moved inward toward the longitudinal axis of the article, decreasing the span between the longitudinal sides by 1.5 cm. The Vertical Deformation test apparatus comprises two clamps having a clamp width (longitudinal length of the clamped portion of the edge of the article) of 5 cm. One clamp is stationary and the other is on a track that permits the clamp to slide to increase or decrease the distance between the clamps while keeping the clamp aligned and parallel to the other clamp. The clamps should be tilted downward at an angle of 20 degrees relative to horizontal, such that both outer edges of the absorbent article are slightly elevated relative to the nearest crease line, thus somewhat simulating the positioning of the outward edges of the absorbent article that may be induced by panties with elevated elastic edges in the crotch region. The clamps are 5 cm above the surface of the track, permitting a pad to be suspended in air between the clamps, gripped in the crotch area such that a portion of the longitudinal sides of the absorbent core are held, with the clamps extending inward no more than about 3 mm from the outer edge of the absorbent core. The article should be held substantially taut in the region between the clamps without damaging the article, such that the crotch region is substantially horizontal before lateral compression begins. At a rate of about 0.5 centimeters per second (cm/s), the slidable clamp is moved smoothly toward the fixed clamp by a distance of 50% of the initial width of the article in the crotch region (or less if the article become incompressible such that more than about 5 kg of force is required to further compress the article). The height of the center of the pad or absorbent article is recorded before the clamp is moved and after the clamp is moved, yielding a difference that is reported as the Vertical Deformation. An increase in height is reported as a positive number, while a decrease is reported as a negative number. Desirably, the Vertical Deformation of the absorbent article is at least about 0.5 cm. Specifically, the Vertical Deformation is at least about 1 cm, and more specifically is at least about 1.5 cm and up to about 10 cm. Desirably, an absorbent article of the present invention exhibits an increase in Vertical Deformation in the crotch region of at least about 20%, and more specifically at least about 50%, relative to the Vertical Deformation in the crotch region exhibited by an essentially identical absorbent article without a shaping line.
As used herein, xe2x80x9cWet Bulkxe2x80x9d is based on a caliper measurement of a sample according to the definition of xe2x80x9cbulkxe2x80x9d above (at 0.344 kPa), except that the conditioned sample is uniformly misted with deionized water until the moistened mass of the sample is approximately 250% of the dry mass of the sample (i.e., the added mass of the moisture is 150% of the dry sample weight). If the sample cannot absorb and retain enough moisture from misting to increase the mass by 150%, then the highest level of achievable moisture add-on below 150% but still above 100% moisture add on should be used. The Wet Bulk in cc/g is calculated as the thickness of the substantially planar moistened sample under a load of 0.344 kPa (0.05 psi) divided by the oven-dry sample basis weight. Absorbent materials in the absorbent members of the present invention can have a Wet Bulk of about 4 cc/g or greater, more specifically about 6 cc/g or greater, more specifically still about 10 cc/g or greater, more specifically still about 10 cc/g or greater, and most specifically about 15 cc/g or greater, with an exemplary range of from about 5 cc/g to about 20 cc/g.